Re: Unique Local Address (ULA) - IPv6

It is somewhat strange.

Essentially they took the FC00::/7 range and subnetted into two /7s --
FC00::/8 and FD00::/8. Each /8 is for a different purpose. Basically we
have two different things because different people have different views on
how things should be done.

With FC00::/8 range your site-local address is actually ASSIGNED to you by a
registrar even though the range is NOT globally routable. This ensures that
everything remains unique within your organization. There is actually
accountability where there is an organization that assigns to you your
locally used ranges

With FD00::/8 it is more like RFC1918 space, where your site-ID is a
"semi-randomly" generated number, and you have 16 bits for subnetting left
which effectively gives you room for like 65,535 /64 subnets to play with :
)

So FC00::/8 looks something like this where the 40-bit global-id (your "site
ID") is ASSIGNED to you

[FC][Global-ID][Subnet-ID][Interface ID]
[8 ] [40 bits ][16 bits ]]64 bits ]

The FD00::/8 stuff would look essentially the same, except the 40-bit
global-id is NOT assigned to you...it is randomly generated

HTH

P.S. This is not to be confused with "site-local" addressing (FEC0::/10)
which is depricated. The reason behind this being depricated has to do with
many many arguments over the ambiguity of what is considered a "site".

On Tue, Dec 15, 2009 at 7:14 PM, Scott Morris <smorris_at_ine.com> wrote:

> You'd configure it where the lab told you. :)
>
> If it said "you have been assigned an ID of ..." then I'd use FC. If it
> said "you decided to use an ID of ...." then I'd use FD.
>
> HTH,
>
>
>
>
> *Scott Morris*, CCIE/x4/ (R&S/ISP-Dial/Security/Service Provider) #4713,
>
> JNCIE-M #153, JNCIS-ER, CISSP, et al.
>
> JNCI-M, JNCI-ER
>
> evil_at_ine.com
>
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>
> Roy Waterman wrote:
> > Hi all
> >
> > Would like some clarification on configuring ulas.
> > We all know its: FC00::/7, however as per RFC4193 it mentions that the L
> bit
> > (the 8th bit) is set to 1 if the prefix is locally assigned, and that L
> bit
> > as 0 is undefined.
> > As such in various places, Ive seen that you'd typically configure ulas
> > starting as fd00::/8, but from a Cisco implementation perspective,
> > does it matter whether fc00::/8 or fd00::/8 is used?
> >
> > >From a lab perspective, if asked to configure a ula, should ipv6 address
> > fd00:... always be used (locally assigning the ipv6 address) ?
> >
> > Please advise.
>
>
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-- 
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